这篇文章主要介绍“PHP高并发之怎么解决商品库存超卖问题”，在日常操作中，相信很多人在PHP高并发之怎么解决商品库存超卖问题问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”PHP高并发之怎么解决商品库存超卖问题”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
高并发对数据库产生的压力
对于第一个问题，使用缓存来处理，避免直接操作数据库，例如使用 Redis。
竞争状态下如何解决商品库存超卖
对于第二个问题，需要重点说明。
常规写法：查询出对应商品的库存，判断库存数量否大于 0，然后执行生成订单等操作，但是在判断库存是否大于 0 处，如果在高并发下就会有问题，导致库存量出现负数。
测试表 sql
把如下表数据导入到数据库中
SET FOREIGN_KEY_CHECKS=0;-- ------------------------------ Table structure for products-- ----------------------------DROP TABLE IF EXISTS `products`;CREATE TABLE `products` ( `id` int(10) NOT NULL AUTO_INCREMENT COMMENT 'ID', `title` varchar(50) DEFAULT NULL COMMENT '货品名称', `store` int(11) DEFAULT '0' COMMENT '货品库存', PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COMMENT='货品表';-- ------------------------------ Records of products-- ----------------------------INSERT INTO `products` VALUES ('1', '稻花香大米', '20');-- ------------------------------ Table structure for order_log-- ----------------------------DROP TABLE IF EXISTS `order_log`;CREATE TABLE `order_log` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `content` varchar(255) CHARACTER SET utf8mb4 DEFAULT NULL COMMENT '日志内容', `c_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '创建时间', PRIMARY KEY (`id`)) ENGINE=MyISAM DEFAULT CHARSET=latin1;-- ------------------------------ Table structure for order-- ----------------------------DROP TABLE IF EXISTS `order`;CREATE TABLE `order` ( `oid` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT '订单号', `product_id` int(11) DEFAULT '0' COMMENT '商品ID', `number` int(11) DEFAULT '0' COMMENT '购买数量', `c_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '创建时间', PRIMARY KEY (`oid`)) ENGINE=MyISAM DEFAULT CHARSET=latin1 COMMENT='订单表';下单处理代码
<?phpdb();global $con;//step1 接收下单参数$product_id = 1;// 商品ID$buy_num = 1;// 购买数量//step2 查询商品信息$sql = "select * from products where id={$product_id}";$result = mysqli_query($con, $sql);$row = mysqli_fetch_assoc($result);//step3 判断商品下单数量是否大于商品库存数量//此处在高并发下，可能出现上一个下单后还没来得及更新库存，下一个下单判断库存数不是最新的库存if ($row['store'] > 0) { sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog('库存减少成功，下单成功'); } else { echo "更新失败"; insertLog('库存减少失败'); }} else { echo "没有库存"; insertLog('库存不够');}function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}function build_order_no(){ return date('Ymd') . str_pad(mt_rand(1, 99999), 5, '0', STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values('$oid', '$product_id', '$number')"; mysqli_query($con, $sql);}function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values('$content')"; mysqli_query($con, $sql);}将库存字段字段设为 unsigned
因为库存字段不能为负数，在下单后更新商品库存时，如果出现负数将返回 false
<?phpdb();global $con;//step1 接收下单参数$product_id = 1;// 商品ID$buy_num = 1;// 购买数量//step2 查询商品信息$sql = "select * from products where id={$product_id} for UPDATE";//利用for update 开启行锁$result = mysqli_query($con, $sql);$row = mysqli_fetch_assoc($result);//step3 判断商品下单数量是否大于商品库存数量if ($row['store'] > 0) { sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog('库存减少成功，下单成功'); } else { // 如果出现负数将返回false echo "更新失败"; insertLog('库存减少失败'); }} else { //商品已经抢购完 echo "没有库存"; insertLog('库存不够');}function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}function build_order_no(){ return date('Ymd') . str_pad(mt_rand(1, 99999), 5, '0', STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values('$oid', '$product_id', '$number')"; mysqli_query($con, $sql);}function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values('$content')"; mysqli_query($con, $sql);}使用 mysql 的事务，锁住操作的行
在下单处理过程中，使用 mysql 的事务将正在下单商品行数据锁定
<?phpdb();global $con;//step1 接收下单参数$product_id = 1;// 商品ID$buy_num = 1;// 购买数量mysqli_query($con, "BEGIN"); //开始事务//step2 查询商品信息$sql = "select * from products where id={$product_id} for UPDATE";//利用for update 开启行锁$result = mysqli_query($con, $sql);$row = mysqli_fetch_assoc($result);//step3 判断商品下单数量是否大于商品库存数量if ($row['store'] > 0) { sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog('库存减少成功，下单成功'); mysqli_query($con, "COMMIT");//事务提交即解锁 } else { echo "更新失败"; insertLog('库存减少失败'); mysqli_query($con, "ROLLBACK");//事务回滚即解锁 }} else { //商品已经抢购完 echo "没有库存"; insertLog('库存不够'); mysqli_query($con, "ROLLBACK");//事务回滚即解锁}function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}function build_order_no(){ return date('Ymd') . str_pad(mt_rand(1, 99999), 5, '0', STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values('$oid', '$product_id', '$number')"; mysqli_query($con, $sql);}function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values('$content')"; mysqli_query($con, $sql);}使用非阻塞的文件排他锁
在处理下单请求的时候，用 flock 锁定一个文件，如果锁定失败说明有其他订单正在处理，此时要么等待要么直接提示用户” 服务器繁忙”，计数器存储抢购的商品数量，避免查询数据库。
阻塞 (等待) 模式：并发时，当有第二个用户请求时，会等待第一个用户请求完成、释放锁，获得文件锁之后，程序才会继续运行下去。
<?phpdb();global $con;//step1 接收下单参数$product_id = 1;// 商品ID$buy_num = 1;// 购买数量$fp = fopen('lock.txt', 'w');if (flock($fp, LOCK_EX)) { //文件独占锁,阻塞 //step2 查询商品信息 $sql = "select * from products where id={$product_id}"; $result = mysqli_query($con, $sql); $row = mysqli_fetch_assoc($result); //step3 判断商品下单数量是否大于商品库存数量 if ($row['store'] > 0) { //处理订单 sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog('库存减少成功，下单成功'); } else { echo "更新失败"; insertLog('库存减少失败'); } } else { //商品已经抢购完 echo "没有库存"; insertLog('库存不够'); } flock($fp, LOCK_UN); //释放锁}fclose($fp);function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}function build_order_no(){ return date('Ymd') . str_pad(mt_rand(1, 99999), 5, '0', STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values('$oid', '$product_id', '$number')"; mysqli_query($con, $sql);}function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values('$content')"; mysqli_query($con, $sql);}非阻塞模式：并发时，第一个用户请求，拿得文件锁之后。后面请求的用户直接返回系统繁忙，请稍后再试
<?phpdb();global $con;//step1 接收下单参数$product_id = 1;// 商品ID$buy_num = 1;// 购买数量$fp = fopen('lock.txt', 'w');if (flock($fp, LOCK_EX|LOCK_NB)) { //文件独占锁,非阻塞 //step2 查询商品信息 $sql = "select * from products where id={$product_id}"; $result = mysqli_query($con, $sql); $row = mysqli_fetch_assoc($result); //step3 判断商品下单数量是否大于商品库存数量 if ($row['store'] > 0) { //处理订单 sleep(1); //step4 更新商品库存数量（减去下单数量） $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "更新成功"; //step5 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog('库存减少成功，下单成功'); } else { echo "更新失败"; insertLog('库存减少失败'); } } else { //商品已经抢购完 echo "没有库存"; insertLog('库存不够'); } flock($fp, LOCK_UN); //释放锁} else { //系统繁忙，请稍后再试 echo "系统繁忙，请稍后再试"; insertLog('系统繁忙，请稍后再试');}fclose($fp);function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}function build_order_no(){ return date('Ymd') . str_pad(mt_rand(1, 99999), 5, '0', STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values('$oid', '$product_id', '$number')"; mysqli_query($con, $sql);}function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values('$content')"; mysqli_query($con, $sql);}因为 pop 操作是原子的，即使有很多用户同时到达，也是依次执行，推荐使用
mysql 事务在高并发下性能下降很厉害，文件锁的方式也是
先将商品库存到 redis 队列
<?phpdb();global $con;// 查询商品信息$product_id = 1;$sql = "select * from products where id={$product_id}";$result = mysqli_query($con, $sql);$row = mysqli_fetch_assoc($result);$store = $row['store'];// 获取商品在redis缓存的库存$redis = new Redis();$result = $redis->connect('127.0.0.1', 6379);$key = 'goods_store_' . $product_id;$res = $redis->llen($key);$count = $store - $res;for ($i=0; $i<$count; $i++) { $redis->lpush($key, 1);}echo $redis->llen($key);function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}抢购、秒杀逻辑
<?phpdb();global $con;//step1 接收下单参数$product_id = 1;// 商品ID$buy_num = 1;// 购买数量//step2 下单前判断redis队列库存量$redis = new Redis();$result = $redis->connect('127.0.0.1',6379);$count = $redis->lpop('goods_store_' . $product_id);if (!$count) { insertLog('error:no store redis'); return '秒杀结束，没有商品库存了';}sleep(1);//step3 更新商品库存数量（减去下单数量）$sql = "update products set store=store-{$buy_num} where id={$product_id}";if (mysqli_query($con, $sql)) { echo "更新成功"; //step4 生成订单号创建订单 $oid = build_order_no(); create_order($oid, $product_id, $buy_num); insertLog('库存减少成功，下单成功');} else { echo "更新失败"; insertLog('库存减少失败');}function db(){ global $con; $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; }}function build_order_no(){ return date('Ymd') . str_pad(mt_rand(1, 99999), 5, '0', STR_PAD_LEFT);}function create_order($oid, $product_id, $number){ global $con; $sql = "INSERT INTO `order` (oid, product_id, number) values('$oid', '$product_id', '$number')"; mysqli_query($con, $sql);}function insertLog($content){ global $con; $sql = "INSERT INTO `order_log` (content) values('$content')"; mysqli_query($con, $sql);}redis 乐观锁防止超卖
<?php$redis =new Redis();$redis->connect("127.0.0.1", 6379);$redis->watch('sales');//乐观锁 监视作用 set() 初始值0$sales = $redis->get('sales');$n = 20;// 库存if ($sales >= $n) { exit('秒杀结束');}//redis开启事务$redis->multi();$redis->incr('sales'); //将 key 中储存的数字值增一 ,如果 key 不存在，那么 key 的值会先被初始化为 0 ，然后再执行 INCR 操作。$res = $redis->exec(); //成功1 失败0if ($res) { //秒杀成功 $con = new mysqli('localhost','root','root','test'); if (!$con) { echo "数据库连接失败"; } $product_id = 1;// 商品ID $buy_num = 1;// 购买数量 sleep(1); $sql = "update products set store=store-{$buy_num} where id={$product_id}"; if (mysqli_query($con, $sql)) { echo "秒杀完成"; }} else { exit('抢购失败');}到此，关于“PHP高并发之怎么解决商品库存超卖问题”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注编程网网站，小编会继续努力为大家带来更多实用的文章！
